Pressure reduction valve is a control valve that lowers the inlet pressure of the fluid and gives the desired pressure at the output. The pressure reduction valve maintains a constant pressure in a part of the system that operates at a pressure lower than the normal system pressure. Often we use a variable pressure reduction valve to set it to any desired downstream pressure within its design range. Once the valve is set, it will maintain reduced pressure regardless of changes in supply pressure and system load variations.

Types of Pressure Reduction Valve

There are numerous designs and types of pressure reducing valves. But most common are:

• The spring-loaded pressure reducing valve
• The pilot-operated pressure reducing valve

Spring Loaded Pressure Reducing Valves

Spring-loaded pressure reducing valve structure and function

The spring-loaded pressure-reducing valve is most commonly used in hydraulic and pneumatic systems. It is generally referred to as a pressure regulator. The valve is normally open all the time. The adjusting spring pressure acts against a diaphragm to open the valve.

When the pressure at the outlet is less than the spring pressure, the spring pressure overcomes the outlet pressure and pulls the valve stem downward. Thus the valve will remain open.

When the outlet pressure is greater than the spring pressure, outlet pressure overcomes the spring pressure and pushes diaphragm and stem upward. Thus the valve will be close.

We can adjust the outlet pressure of the valve by adjusting spring pressure on the diaphragm. Normally, when we turn the adjusting screw clockwise, we are increasing the downstream pressure.

Pilot-Operated Pressure Reducing Valve

The simple diagram above illustrates a pilot operated pressure reducing valve. This valve is similar to the spring-loaded valve in addition to the pilot-controlled valve. High pressure will come from the pump to the inlet port. Normally due to the open condition, the oil will flow to the outlet port. Actually, the pressure at the outlet depends on the spring pressure of the reducing valve.

When pressure builds up at the outlet it will act on the bottom of the main spool. Simultaneously, a pilot pressure acts on the ball against a spring-2 and spring chamber through an orifice. This pressure keeps the main spool open until the pressure at the outlet port is less than the pressure at Spring-2. If the outlet pressure is above the set pressure of spring 2, the ball will move forward and the pilot line will connect with the tank. This will empty the spring chamber and the main spool will move upward and close the inlet port. Thus, a pilot operated pressure reducing valve works.

Pressure reducing valve Symbols

References

• ScienceDirect

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The industrial hydraulic symbol or just the hydraulic symbol is the first step towards an understanding of the hydraulic system. Without a basic understanding of symbols, one cannot efficiently troubleshoot the hydraulic system completely. A hydraulic system consists of cylinders, motors, valves, and pumps connected via hydraulic hoses and pipes. Due to the complexity of showing these components in a diagram we use symbols instead of absolute components.

Industrial Hydraulic Symbol

Most hydraulic industries follow standard DIN ISO 1219 for the design of hydraulic circuits, however, one can find differences in individual drawings with the company.

The symbols in a hydraulic schematic give the following information about the system:

1. Type of Prime mover (Engine or Electric Motor)
2. General information about pump (CC/rev & RPM)
3. The number of connections and joints for the representation of the hydraulic flow.
4. Different types of valve and their functions.
5. The number of switching positions of the valves.
6. Actuation and return method of the valves.

Although we get all necessary information from schematic and symbols, it can define the following details:

1. The exact location of the components.
2. Dimensions of the component.
3. Manufacturer of the components.

Now, by keeping the intention of a hydraulic schematic in mind, one can understand the basic symbol for the hydraulic system very easily.

Basic hydraulic symbols

	Pressure line or Return line.
	Quick release coupling.
	Shuttle Valve.
	Pressure Gauge.
	Multiport Swivel.
	Manifold
	Line Junction.
	Connection for measuring port.

Symbols for actuation type

	Actuation by pneumatic (compressed air).
	Actuation by spring force.
	Actuation by Hydraulic pressure.
	Actuation by the plunger.
	Actuation by the roller movement.
	Actuation by solenoid (electrically)
	Actuation by electro-hydraulically.
	Actuation by foot paddle.
	Actuation by a lever.

Symbols for filters and coolers

	Filter
	Cooler

Symbols for Valves

	Pressure Relief Valve (non-adjustable)
	Pressure relief Valve (adjustable)
	Check Valve
	Pilot Operated Check Valve.
	Pressure reducing Valve
	3 Port Pressure Reducing Valve

Symbols for Pump and Motor

	Mono direction fix displacement pump
	Mono direction variable displacement pump
	Mono direction fix displacement motor
	Mono direction variable displacement motor
	Bi-directional fix displacement pump
	Bi-direction variable displacement pump
	Bi-direction fix displacement motor
	Bi-direction variable displacement motor
	Electric Motor

Symbols for Cylinders

	Single Acting Cylinder
	Double Acting Cylinder
	Telescopic Cylinder

FAQ

(Que.1) What is the hydraulic symbol for concrete pumps?

Answer: The symbol will be the same for all pumps. Concrete pumps are designed differently because it has to handle dense liquid or semi-solid materials, but the symbol will be similar. See the Symbol

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